U.S. patent application number 13/251086 was filed with the patent office on 2012-10-11 for multilayer rare earth device.
This patent application is currently assigned to Translucent, Inc.. Invention is credited to F. Erdem Arkun, Andrew Clark, Michael Lebby.
Application Number | 20120256232 13/251086 |
Document ID | / |
Family ID | 46965416 |
Filed Date | 2012-10-11 |
United States Patent
Application |
20120256232 |
Kind Code |
A1 |
Clark; Andrew ; et
al. |
October 11, 2012 |
Multilayer Rare Earth Device
Abstract
Examples of device structures utilizing layers of rare earth
oxides to perform the tasks of strain engineering in transitioning
between semiconductor layers of different composition and/or
lattice orientation and size are given. A structure comprising a
plurality of semiconductor layers separated by transition layer(s)
comprising two or more rare earth compounds operable as a sink for
structural defects is disclosed.
Inventors: |
Clark; Andrew; (Palo Alto,
CA) ; Arkun; F. Erdem; (Palo Alto, CA) ;
Lebby; Michael; (Palo Alto, CA) |
Assignee: |
Translucent, Inc.
Palo Alto
CA
|
Family ID: |
46965416 |
Appl. No.: |
13/251086 |
Filed: |
September 30, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12619621 |
Nov 16, 2009 |
8049100 |
|
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13251086 |
|
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Current U.S.
Class: |
257/190 ;
257/E29.068 |
Current CPC
Class: |
H01L 21/02532 20130101;
Y02P 70/521 20151101; Y02E 10/547 20130101; H01L 31/0725 20130101;
H01L 21/02381 20130101; H01L 31/0745 20130101; H01L 21/02488
20130101; H01L 21/0245 20130101; H01L 31/1804 20130101; H01L
21/02502 20130101; Y02P 70/50 20151101; H01L 21/02507 20130101;
H01L 21/02422 20130101 |
Class at
Publication: |
257/190 ;
257/E29.068 |
International
Class: |
H01L 29/12 20060101
H01L029/12 |
Claims
1. A solid state device comprising; a first semiconductor layer; a
second semiconductor layer; and a transparent layer consisting of a
plurality of rare earth compounds; wherein the transparent layer
separates the first semiconductor layer and the second
semiconductor layer such that the composition of the transparent
layer adjacent the first semiconductor layer is different than the
composition of the transparent layer adjacent the second
semiconductor layer.
2. The solid state device of claim 1 wherein the composition of the
transparent layer adjacent the first semiconductor layer is chosen
such that a predetermined stress is introduced into the portion of
the first semiconductor layer adjacent the transparent layer and
the composition of the transparent layer adjacent the second
semiconductor layer is chosen such that a predetermined stress is
introduced into the portion of the second semiconductor layer
adjacent the transparent layer and the stress in the portion of the
first semiconductor layer adjacent the transparent layer is
different than the stress in the portion of the second
semiconductor layer adjacent the transparent layer.
3. The solid state device of claim 1 wherein the plurality of rare
earth compounds are of a composition described by
[RE1].sub.x[RE2].sub.y[J].sub.z wherein RE1 and RE2 are different
rare earths; J is one of oxygen, nitrogen or phosphorus; and x, y,
z>0.
4. The solid state device of claim 1 wherein the plurality of rare
earth compounds are of a composition described by
[RE1].sub.x[RE2].sub.y[J1].sub.z[J2].sub.w wherein RE1 and RE2 are
different rare earths; J1 and J2 are chosen from oxygen, nitrogen
and phosphorus; and w, x, y, z>0.
5. The solid state device of claim 1 wherein the plurality of rare
earth compounds are of a composition described by
(RE1.sub.xRE2.sub.1-).sub.2O.sub.3 wherein RE1 and RE2 are
different rare earths; and O is oxygen.
6. The solid state device of claim 1 wherein the first and second
semiconductor layers are of a composition chosen from Group II,
III, IV, V and VI elements.
7. The solid state device of claim 2 wherein the composition of the
transparent layer adjacent the first semiconductor layer is chosen
such that the lattice constant, x, of the rare earth compounds is
between about 1.95(y).ltoreq.x.ltoreq.1.99(y) and about
2.01(y).ltoreq.x.ltoreq.2.05(y) wherein y is the lattice constant
of the first semiconductor layer such that the predetermined stress
is introduced into the portion of the first semiconductor layer
adjacent the transparent layer.
8. The solid state device of claim 2 wherein the composition of the
transparent layer adjacent the second semiconductor layer is chosen
such that the lattice constant, v, of the rare earth compounds is
between about 1.95(w).ltoreq.v.ltoreq.1.99(w) and about
2.01(w).ltoreq.v.ltoreq.2.05(w) wherein w is the lattice constant
of the second semiconductor layer such that the predetermined
stress is introduced into the portion of the second semiconductor
layer adjacent the transparent layer.
9. The solid state device of claim 1 wherein the plurality of rare
earth compounds are of a composition described by
[RE1].sub.x[RE2].sub.y[J].sub.z wherein RE1 and RE2 are different
rare earths; J is one of oxygen or phosphorus; and x, y,
z>0.
10. The solid state device of claim 1 wherein the device is chosen
from a group consisting of LEDs, lasers, photovoltaics, inverters,
and devices comprising a heterojunction.
11. A solid state device comprising; a first semiconductor layer; a
second semiconductor layer; and a transparent layer consisting of a
plurality of rare earth compounds; wherein the transparent layer
separates the first semiconductor layer and the second
semiconductor layer such that a predetermined stress is introduced
into the portion of the first semiconductor layer adjacent the
transparent layer by selecting a composition of the transparent
layer adjacent the first semiconductor layer such that the lattice
constant, x, of the rare earth compounds adjacent the first
semiconductor layer is between about
1.95(y).ltoreq.x.ltoreq.1.99(y) and about
2.01(y).ltoreq.x.ltoreq.2.05(y) wherein y is the lattice constant
of the first semiconductor layer and such that a predetermined
stress is introduced into the portion of the second semiconductor
layer adjacent the transparent layer by selecting a composition of
the transparent layer adjacent the second semiconductor layer such
that the lattice constant, v, of the rare earth compounds adjacent
the second semiconductor layer is between about
1.95(w).ltoreq.v.ltoreq.1.99(w) and about
2.01(w).ltoreq.v.ltoreq.2.05(w) wherein w is the lattice constant
of the second semiconductor layer.
12. The solid state device of claim 11 wherein the plurality of
rare earth compounds is chosen from rare earth oxides, phosphides,
oxy-nitrides, oxy-phosphides and phosphide-nirtrides.
Description
PRIORITY
[0001] This application is a continuation-in-part of application
Ser. No. 12/619,621, filed on Nov. 16, 2009, and claims priority
from that application.
CROSS REFERENCE TO RELATED APPLICATIONS
[0002] Applications and patents 11/025,692, 11/025,693,
U.S.20050166834, 11/253,525, 11/257,517, 11/257,597, 11/393,629,
11/472,087, 11/559,690, 11/599,691, 11/788,153, 11/828,964,
11/858,838, 11/873,387 11/960,418, 11/961,938, 12/119,387,
60/820,438, 61/089,786, 12/029,443, 12/046,139, 12/111,568,
12/119,387, 12/171,200, 12/408,297, 12/510,977, 60/847,767, U.S.
Pat. No. 6,734,453, U.S. Pat. No. 6,858,864, U.S. Pat. No.
7,018,484, U.S. Pat. No. 7,023,011 U.S. Pat. No. 7,037,806, U.S.
Pat. No. 7,135,699, U.S. Pat. No. 7,199,015, U.S. Pat. No.
7,211,821, U.S. Pat. No. 7,217,636, U.S. Pat. No. 7,273,657, U.S.
Pat. No. 7,253,080, U.S. Pat. No. 7,323,737, U.S. Pat. No.
7,351,993, U.S. Pat. No. 7,355,269, U.S. Pat. No. 7,364,974, U.S.
Pat. No. 7,384,481, U.S. Pat. No. 7,416,959, U.S. Pat. No.
7,432,569, U.S. Pat. No. 7,476,600, U.S. Pat. No. 7,498,229, U.S.
Pat. No. 7,586,177, U.S. Pat. No. 7,599,623, U.S.Pat. No. 8,039,738
and U.S. Applications Ser. Nos. 12/890,537, 12/619,621, 12/619,549,
all held by the same assignee, contain information relevant to the
instant invention and are incorporated herein in their entirety by
reference. References, noted in the specification and Information
Disclosure Statement, are incorporated herein in their entirety by
reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The invention relates generally to a semiconductor based
structure for transitioning from one semiconductor material
composition to another by the use of one or more transition layers
comprising more than one rare earth enabling devices such as LEDs,
lasers, photovoltaics, inverters, and devices comprising a
heterojunction.
[0005] 2. Description of Related Art Including Information
Disclosed Under 37 CFR 1.97 and 1.98.
[0006] One approach to improve efficiency in a solar cell is
multiple junctions where specific materials are matched to discrete
portions of the solar spectrum. For example it is widely accepted
that a single junction, single crystal silicon solar cell has an
optimum performance in the wavelength range 500 to 1,100 nm, whilst
the solar spectrum extends from 400 nm to in excess of 2,500
nm.
[0007] As used herein a rare earth, [RE1, RE2, . . . RE.sub.n], is
chosen from the lanthanide series of rare earths from the periodic
table of elements {.sup.57La, .sup.58Ce, .sup.59Pr, .sup.60Nd,
.sup.61Pm, .sup.62Sm, .sup.63Eu, .sup.64Gd, .sup.65Tb, .sup.66Dy,
.sup.67Ho, .sup.68Er, .sup.69Tm, .sup.70Yb and .sup.71Lu} plus
yttrium, .sup.39Y, and scandium, .sup.21Sc, are included as well
for the invention disclosed.
[0008] As used herein a transition metal, [TM1, TM2 . . .
TM.sub.n], is chosen from the transition metal elements consisting
of {.sup.22Ti, .sup.23V, .sup.24Cr, .sup.25Mn, .sup.26Fe,
.sup.27Co, .sup.28Ni, .sup.29Cu, .sup.30Zn, .sup.40Zr, .sup.41Nb,
.sup.42Mo, .sup.43Tc, .sup.44Ru, .sup.45Rh, .sup.46Pd, .sup.47Ag,
.sup.48Cd, .sup.71Lu, .sup.72Hf, .sup.73Ta, .sup.74W, .sup.75Re,
.sup.76OS, .sup.77Ir, .sup.78Pt, .sup.77Au, .sup.80Hg }. Silicon
and germanium refer to elemental silicon and germanium; Group IV,
Groups III and V and Groups II and VI elements have the
conventional meaning. As used herein all materials and/or layers
may be present in a single crystalline, polycrystalline,
nanocrystalline, nanodot or quantum dot and amorphous form and/or
mixture thereof.
[0009] In addition certain of these rare earths, sometimes in
combination with one or more rare earths, and one or more
transition metals can absorb light at one wavelength (energy) and
re-emit at another wavelength (energy). This is the essence of
wavelength conversion; when the incident, adsorbed, radiation
energy per photon is less than the emission, emitted, energy per
photon the process is referred to as "up conversion". "Down
conversion" is the process in which the incident energy per photon
is higher than the emission energy per photon. An example of up
conversion is Er absorbing at 1,480 nm and exhibiting
photoluminescence at 980 nm.
[0010] U.S. Pat. No. 6,613,974 discloses a tandem Si--Ge solar cell
with improved efficiency; the disclosed structure is a silicon
substrate onto which a Si--Ge epitaxial layer is deposited and then
a silicon cap layer is grown over the Si--Ge layer; no mention of
rare earths is made. U.S. Pat. No. 7,364,989 discloses a silicon
substrate, forming a silicon alloy layer of either Si--Ge or Si--C
and the depositing a single crystal rare earth oxide, binary or
ternary; the alloy content of the alloy layer is adjusted to select
a type of strain desired; the preferred type of strain is
"relaxed"; the preferred deposition method for the rare earth oxide
is atomic layer deposition at temperatures below 300.degree. C.
While the Si--Ge film is "relaxed", its primary function is to
impart no strain, tensile strain or compressive strain to the rare
earth oxide layer; the goal being to improve colossal
magnetoresistive, CMR, properties of the rare earth oxide. A
preferred method disclosed requires a manganese film be deposited
on a silicon alloy first. Recent work on rare earth films deposited
by an ALD process indicate the films are typically polycrystalline
or amorphous.
BRIEF SUMMARY OF THE INVENTION
[0011] Examples of device structures utilizing layers of rare earth
oxides to perform the tasks of strain engineering in transitioning
between semiconductor layers of different composition and/or
lattice orientation or size. A structure comprising a plurality of
semiconductor layers separated by two or more rare earth based
transition layers operable as a sink for structural defects is
disclosed. One advantage of thin films is the control provided over
a process both in tuning a material to a particular wavelength and
in reproducing the process in a manufacturing environment. In some
embodiments, rare earth oxides, nitrides, and phosphides,
transition metals and silicon/germanium materials and various
combinations thereof may be employed. As used herein the terms,
"oxides" and "rare-earth oxide[s]" are inclusive of rare earth
oxides, nitrides, and phosphides and combinations thereof.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0012] FIG. 1a: Prior art for triple junction cell on Ge substrate;
FIG. 1b triple junction cell on Ge bonded to Si wafer.
[0013] FIG. 2a shows unit cell size versus Ge content in SiGe
alloy, FIG. 2b: schematic definition of mismatch between Ge and Si
layers; FIG. 2c shows exemplary REO transition layer facilitating
Si to Ge layers.
[0014] FIG. 3: Relationship between rare earth lattice spacing and
lattice spacing of Ge and Si
[0015] FIG. 4: Examples of ternary RE alloys, relationship of
lattice spacing to alloy composition
[0016] FIG. 5: Calculations of specific RE alloys relative to
lattice spacing of various SiGe alloys
[0017] FIG. 6a: unit cells lattice matched at each interface; FIG.
6b shows calculation of internal layer stress.
[0018] FIG. 7a: Exemplary unit cell with lattice mismatched
interfaces; FIG. 7b shows calculation of internal layer stress
versus RE composition.
[0019] FIGS. 8a and 8b: Examples of RE grading used in REO
layer.
[0020] FIG. 9: Example of multiple cells in a Ge--Si-REO engineered
structure.
[0021] FIG. 10a: Specific embodiment of a unit cell, FIG. 10b
accompanying x-ray measurement.
[0022] FIG. 11: Example of strain symmetrized superlattice (SSSL)
using group IV-RE alloys.
[0023] FIG. 12a: Specific embodiment of strain symmetrized
superlattice (SSSL); FIG. 10b magnified superlattice structure.
[0024] FIG. 13: X-ray result for SSSL
[0025] FIG. 14a is a side view of two semiconductor layers with
stressed layers between; FIG. 14b is a side view of an embodiment
in which stressed rare-earth based layers enable a product
comprising silicon and germanium layers.
DETAILED DESCRIPTION OF THE INVENTION
[0026] A substrate may be a semiconductor, such as silicon, and be
poly or multi-crystalline, silicon dioxide, glass or alumina. As
used herein multi-crystalline includes poly, micro and nano
crystalline. "A layer" may also comprise multiple layers. For
example, one embodiment may comprise a structure such as:
substrate/[REO]
1/Si(1-x)Ge(x)/[REO]2/Si(1-y)Ge(y)/[REO]3/Si(1-z)Ge(z); wherein
[REO]1 is one or more rare earth compounds and one or more layers
in a sequence proceeding from a substrate to a first Group IV based
compound, Si(1-x)Ge(x), and on to a Group IV based semiconductor
top layer; Group III-V and II-VI and combinations thereof are also
possible embodiments. Disclosed layers are, optionally, single
crystal, multi-crystalline or amorphous layers and compatible with
semiconductor processing techniques. As used herein a "REO" layer
contains two or more elements, at least one chosen from the
Lanthanide series plus Scandium and Yttrium and at least one chosen
from oxygen and/or nitrogen and/or phosphorous and/or mixtures
thereof; structures are not limited to specific rare-earth elements
cited in examples. Rare earth materials are represented as
(RE1+RE2+ . . . REn).sub.mO.sub.n where the total mole fraction of
rare earths, 1 . . . n, is one for stoichiometric compounds and not
limited to 1 for non-stoichiometric compounds. In some embodiments,
in addition to the RE (1, 2, . . . n) an alloy may include Si
and/or Ge and/or C, carbon; optionally an oxide may be an
oxynitride or oxyphosphide; m and n may vary from greater than 0 to
5.
[0027] In some embodiments a low cost substrate such as soda glass
or polycrystalline alumina is used in combination with a rare-earth
based structure comprising a diffusion barrier layer, a buffer
layer, an active region, up and/or down layer(s), one or more
reflectors, one or more Bragg layers, texturing is optional; one or
more layers may comprise a rare-earth. The exact sequence of the
layers is application dependent; in some cases for a solar cell,
sunlight may enter a transparent substrate initially; in other
cases a transparent substrate may be interior of multiple
layers.
[0028] FIGS. 1a and 1b illustrate prior art embodiments; FIG. 1a
shows schematically a III-V triple junction cell on a Ge substrate.
FIG. 1b shows schematically a Ge based junction on an insulator
bonded to a Si wafer; both approaches are expensive and have
limitations. FIG. 2a Shows the lattice constant, a, of a
silicon-germanium alloy, Si.sub.1-xGe.sub.x as x varies from 0, all
silicon, to 1, all germanium. FIG. 2b shows schematically the
relative difference between Si and Ge unit cells; Ge being about
4.2% larger than Si. FIG. 2c shows schematically a REO based
engineered structure; an exemplary embodiment, as shown in FIG. 2c,
is a structure comprising a silicon substrate, REO based layer(s),
a germanium layer and, optionally, one or more layers overlying the
Ge layer; optionally, a semiconductor, optionally silicon,
substrate may comprise one or more junctions operable as a solar
cell or other device(s); optionally, the germanium layer(s) may
comprise one or more junctions operable as a solar cell or other
device(s); optionally, the REO layer(s) may comprise one or more
layers operable as a diffusion barrier layer, a buffer layer and a
transition layer. FIG. 9 shows another exemplary embodiment.
[0029] FIG. 3 shows lattice spacing, a, for different rare earths
as compared to Si and Ge. FIG. 4 shows how the lattice constant for
three erbium based rare earth alloys vary as a function of
composition and choice of a second rare earth component versus
twice the lattice constant of silicon. (Er.sub.1-xLa.sub.x)O.sub.3,
(Er.sub.1-xPr.sub.x)O.sub.3, (Er.sub.1-xEu.sub.x)O.sub.3 are chosen
for this example; other combinations are acceptable also. Exemplary
structures include bulk ternary alloys as listed or an alternating,
"digital" superlattice of n(Er.sub.2O.sub.3)/m(Eu.sub.3O.sub.3,
comprising a repeat unit where the average "x-value", x=m/(n+m).
Unstable valence rare earths, such as Eu, Pr and La, can be
stabilized to a 3+ valence state when alloyed with
(Er.sub.2O.sub.3) for 0.ltoreq.x<x.sub.crit, where x.sub.crit is
where the onset of phase transformation or valence instability
re-occurs.
[0030] FIG. 5 shows lattice spacing, a, of different SiGe alloys
versus lattice spacing for different rare earth alloys as a
function of composition. FIG. 6a is an exemplary structure with a
ternary rare earth transitioning between a semiconductor layer or
substrate and a Si.sub.1-xGe.sub.x layer. FIG. 6b shows the
variation in the lattice constant as the rare earth based layer
lattice constant transitions from 2a.sub.Si to 2a.sub.Si1-xGex
based on a.sub.RE1ylRE21-yl and a.sub.RE1y2RE21-y2 of initial rare
earth compound RE1.sub.y1RE2.sub.1-ylO.sub.3 and final rare earth
compound RE1.sub.y2RE2.sub.1-y2O.sub.3. FIGS. 7a and 7b show
alternative embodiments where a rare earth layer may be of somewhat
different lattice constant than a silicon or SiGe alloy or
germanium layer resulting in compressive or tensile strains in the
respective layers. FIG. 8a is an exemplary example for a rare earth
based layer of (Gd.sub.0.82Nd.sub.0.18).sub.2O.sub.3 transitioning
linearly to (Gd.sub.0.35Nd.sub.0.65).sub.2O.sub.3 between a silicon
surface to a layer of Si.sub.0.3Ge.sub.0.7. FIG. 8b is an exemplary
example for a rare earth based layer of
(Er.sub.0.46La.sub.0.54).sub.2O.sub.3 transitioning in a stepwise
or digital fashion to (Er.sub.0.24La.sub.0.76).sub.2O.sub.3 between
a Si.sub.0.3Ge.sub.0.7 surface to a layer of Si.sub.0.7Ge.sub.0.3.
As disclosed herein a rare earth based transition layer may be a
binary, ternary quaternary or higher rare earth compound of
composition described by
[RE1].sub.v[RE2].sub.w[RE3].sub.x[J1].sub.y[J2].sub.z wherein [RE]
is chosen from a rare earth; [J1] and [J2] are chosen from a group
consisting of Oxygen (O), Nitrogen (N), and Phosphorus (P) , and
0.ltoreq.v, w, z.ltoreq.5, and 0<x, y.ltoreq.5.
[0031] FIG. 9 is an exemplary embodiment showing a structure 900
starting with a first semiconductor layer 905, optionally, silicon,
a first transition layer 910 of composition
(RE1.sub.xRE2.sub.1-x).sub.2O.sub.3, a second semiconductor layer
915, a second transition layer 920, a third semiconductor layer
925, a third transition layer 930, and a fourth semiconductor layer
935, optionally, germanium. In general RE1 is different from RE2;
however RE3, RE4, RE5, and RE6 need not be different from RE1
and/or RE2. Semiconductor layers 905, 915, 925 and 935 may be one
or more Group IV materials; optionally, one or more Group III-V
materials; optionally, one or more Group II-VI materials. In some
embodiments the semiconductor layers are operable as solar cells
tuned to different portions of the solar spectrum. In preferred
embodiments transition layers 910, 920, 930 enable stress
engineering between the semiconductor layers.
[0032] FIG. 10a is an exemplary example of a single composition
layer of (Gd.sub.0.75Nd.sub.0.25).sub.2O.sub.3 transitioning
between a silicon layer and a Si.sub.0.95Ge.sub.0.5 layer. FIG. 10b
shows an x-ray scan of the structure showing the intensity of the
substrate and layer peaks indicating the close lattice match.
[0033] FIG. 11 shows x-ray diffraction patterns of silicon as
unstrained cubic, of a Si.sub.0.8Ge.sub.0.2 in biaxial compression
and two Si-rare earth alloys in biaxial tension. These are examples
of layer composition combinations for achieving strain symmetry in
a superlattice type structure; also referred to as a strain
symmetrized superlattice. FIG. 12a is a TEM of an exemplary
structure; FIG. 12b is a magnification of the superlattice portion
exhibiting strain symmetry. Additional information is found in U.S.
application Ser. No. 11/828,964. FIG. 13 is an x-ray scan of a
strain symmetrized superlattice structure.
[0034] FIGS. 14a and b show an embodiment of a strain symmetrized
structure 1400 with a Semiconductor B, optionally silicon, based
lower layer and a Semiconductor A, optionally germanium, based
upper layer. Referring additionally to FIGS. 14a and 14b, with
individual layers or films 1410 and 1420 forming a composite layer
1400, in accordance with the present invention. Layer 1410 has a
width designated d.sub.a and layer 1420 has a width designated
d.sub.b. Layer 1410 has a bulk modulus Ma and layer 1420 has a bulk
modulus Mb. To provide a desired composite stress in the composite
layer 1400, the individual thicknesses (d.sub.a and d.sub.b)
required in each layer 1410 and 1420 can be calculated based on
stress energy at the interface. Layer 1410 and 1420 may be
separated by a third layer, not shown, to enhance the functionality
of composite layer 1400 as a sink for lattice defects and/or
functionality as an up and/or down converter of incident radiation.
In some embodiments d.sub.a and d.sub.b may be about 2 nm; in some
embodiments d.sub.a and d.sub.b may be about 200 nm; alternatively,
d.sub.a and d.sub.b may be between about 2 to about 200 nm; a third
layer, not shown, may be between about 2 to about 200 nm.
[0035] Referring to FIG. 14b, a specific example of a structure
including a exemplary germanium semiconductor layer on a composite
rare earth layer 1400, in accordance with the present invention, is
illustrated. It is known that germanium has a large thermal and
lattice mismatch with silicon. However, in many applications it is
desirable to provide crystalline germanium active layers on silicon
layers. In the present example, stressed layer 1410 of composite
insulating layer 1400 is adjacent a germanium layer and stressed
layer 1420 is adjacent a silicon layer. Stressed layers 1410 and
1420 are engineered (e.g. in this example highly stressed) to
produce a desired composite stress in composite layer 1400. In some
embodiments, compositions of stressed insulating layers 1410 and
1420 are chosen to reduce thermal mismatch between first and second
semiconductor layers also.
[0036] In one embodiment rare earth oxide layers are also
performing a task of strain balancing, such that the net strain in
the REO/Si(1-y)Ge(y) composite layer is effectively reduced over
that of a single REO layer of the same net REO thickness grown on
the same substrate, thus allowing a greater total thickness of REO
to be incorporated into the structure before the onset of plastic
deformation. In another embodiment rare earth oxide layers are
strain balanced such that a critical thickness of the
REO/Si(1-y)Ge(y) composite is not exceeded. In another embodiment
REO/Si(1-y)Ge(y) composite layer acts to mitigate propagation of
dislocations from an underlying Si(1-x)Ge(x) layer through to the
overlying Si(1-z)Ge(z) layer thereby improving the crystallinity
and carrier lifetime in the Si(1-z)Ge(z) layer. In another
embodiment, the Si(1-x)Ge(x) has a narrower band gap than the
Si(1-z)Ge(z) layer (i.e. x>z) such that the Si(1-z)Ge(z) layer
and the Si(1-x)Ge(x) layers form a tandem solar cell. For example,
solar radiation impinges upon the Si(1-z)Ge(z) layer first where
photons of energy greater than the band gap of Si(1-z)Ge(z) are
absorbed and converted to electrical energy. Photons with energy
less than the band gap of Si(1-z)Ge(z) are passed through to the
Si(1-x)Ge(x) layer where a portion may be absorbed. In one
embodiment rare earth oxide layers are performing a task of strain
balancing, such that the net strain in the REO/Si(1-y)Ge(y)
composite layer is effectively reduced over that of a single REO
layer of the same net REO thickness grown on the same
substrate.
[0037] In some embodiments a device comprises a Group IV
semiconductor based superlattice comprising a plurality of layers
that form a plurality of repeating units, wherein at least one of
the layers in the repeating unit is a layer with at least one
species of rare earth ion wherein the repeating units have two
layers comprising a first layer comprising a rare earth compound
described by([RE1].sub.x[RE2].sub.z).sub.w[J1].sub.y[J2].sub.u and
a second layer comprising a compound described by
Si.sub.(1-m)Ge.sub.m wherein x, y>0, m.gtoreq.0, 0.ltoreq.u, w,
z.ltoreq.3 and J is chosen from oxygen, nitrogen, phosphorous and
combinations thereof.
[0038] In some embodiments a device comprises a superlattice that
includes a plurality of layers that form a plurality of repeating
units, wherein at least one of the layers in the repeating unit is
a layer with at least one species of rare earth ion wherein the
repeating units comprise two layers wherein the first layer
comprises a rare earth compound described by [RE1].sub.x[J].sub.y
and the second layer comprises a compound described by
((RE2.sub.mRE3.sub.n).sub.oJ.sub.p wherein m, n, o, p, x, y>0
and J is chosen from a group comprising oxygen, nitrogen,
phosphorous and combinations thereof; optionally, RE1, RE2 and RE3
may refer to the same or different rare earths in different
repeating units.
[0039] As known to one knowledgeable in the art, a photovoltaic
device may be constructed from a range of semiconductors including
ones from Group IV materials, Group III-V materials and Group
II-VI; additionally, photovoltaic devices such as a laser, LED and
OLED may make advantageous use of the instant invention for
transitioning between different semiconductor layers; for instance,
GaN on Si can be used for high voltage power FET's; these devices
are used in inverters in the solar and electric vehicle markets for
reduced power consumption and higher operating efficiency.
[0040] It is well known that multiple junction solar cells are
capable of reaching higher conversion efficiencies than single
junction cells, by extracting electrons at an energy closer to the
original photon energy that produced the electron. In this
invention we describe the use of single or polycrystalline
Si(1-x)Ge(x) alloys in combination with single crystal or
polycrystalline silicon such that a two or more junction or
`tandem` cell is realized. The monolithic SiGe/Si structure is
enabled through the use of a rare-earth oxide transition layer(s)
between the Si and SiGe as shown in FIG. 9. REO layers 910, 920,
930 may be one or a plurality of
[RE1].sub.n[RE2].sub.b[RE3].sub.c[O].sub.g[P].sub.h[N].sub.i type
layers.
[0041] An example of a doping and interconnect scheme is where the
rear p-type region of a silicon cell is connected through to the
p-type region of the SiGe cell by a metalized via through a REO
channel. Alternatively a REO layer 910 may be doped to form a
conductive buffer layer between Si and SiGe. Other embodiments are
also possible, for example where the p and n doping regions are
reversed and a tunnel junction is used to create a two terminal
device, rather than a three terminal device, as shown. Also
possible is a device where the front metal contact and n-type
doping region is placed at the back of the silicon layer, with a
similar via contact scheme as is shown for the p-type silicon
region. SiGe has a crystal lattice constant different to Si, such
that when SiGe is deposited epitaxially directly on Si, the SiGe
layer is strained. As the SiGe layer is grown thicker, the strain
energy increases up to a point where misfit dislocations are formed
in the SiGe film, which negatively impact performance of devices,
including solar cell devices. In this invention, a REO buffer or
transition layer may serve as a strain relief layer between Si and
SiGe, such that misfit dislocations are preferentially created in
the REO layer, thus reducing the dislocation density in the SiGe
layer. The REO layer may also have compositional grading such that
the REO surface in contact with the silicon layer is lattice
matched to silicon, while the REO surface in contact with the SiGe
layer is lattice matched to SiGe. For example,
(Gd.sub.0.81Nd.sub.0.19).sub.2O.sub.3 has a lattice spacing of
10.863 .ANG., which is about twice the lattice spacing of silicon
(10.8619 .ANG.). For Si0.43Ge0.57, the bandgap is 0.884 eV which
allows the SiGe layer to absorb solar radiation in the band between
1100 to 1400 nm. Twice the lattice spacing of
Si.sub.0.43Ge.sub.0.57 is 11.089 .ANG. which is close to the
lattice spacing of Nd.sub.2O.sub.3 (11.077 .ANG.). Thus, by grading
the composition of the REO layer from
(Gd.sub.0.81Nd.sub.0.19).sub.2O.sub.3 to Nd.sub.2O.sub.3, the
strain and dislocation network may be confined to the REO layer,
thereby increasing the carrier lifetime and performance of the SiGe
cell over that which would be obtained if the SiGe were grown
directly on the Si. The instant invention discloses the use of a
rare earth transition layer to function as a sink or getter for
lattice defects created by the lattice mismatch between a first
semiconductor layer and a rare earth layer transitioning to a
second semiconductor layer.
[0042] X-ray diffraction measurements were performed by using a
Phillips X'pert Pro four circle diffractometer. Incident Cu Kal
beam was conditioned using a Ge (220) four-bounce monochromator;
diffracted beam was passed through a channel cut, two bounce (220)
Ge analyzer in order to achieve higher resolution. The Bragg
reflection from the Si (111) planes was measured to analyze the
lattice parameter of the grown structure. X-ray diffraction
spectrum shows intensity modulations around the fundamental
reflections of the substrate, indicating a smooth epitaxial layer
terminally.
[0043] In prior art of the same assignee a rare earth based
structure is disclosed comprising a first and second region wherein
the first region has a first and second surface and the second
region has a first and second surface; and the second region has a
composition of the form
[RE1].sub.v[RE2].sub.w[RE3].sub.x[J1].sub.y[J2].sub.z, wherein [RE]
is chosen from the disclosed rare earth group; [J1] and [J2] are
chosen from a group consisting of oxygen (O), nitrogen (N), and
phosphorus (P) ; wherein 0.ltoreq.v, z.ltoreq.5; and 0<w, x,
y.ltoreq.5 such that the second region has a composition different
from the first region and wherein the first surface of the second
region is in direct contact with the second surface of the first
region and the first region is comprised of a composition of the
form [RE1].sub.a[RE2].sub.b[RE3].sub.c[J1].sub.d[J2].sub.e, wherein
[RE] is chosen from the disclosed rare earth group; [J1] and [J2]
are chosen from a group consisting of oxygen (O), nitrogen (N), and
phosphorus (P); wherein 0.ltoreq.b, c, e.ltoreq.5; and 0<a,
d.ltoreq.5. The structure as disclosed may be used in conjunction
with similar structures additionally comprising a transition metal,
TM and, optionally comprising a Group IV element or mixtures
thereof.
[0044] In some embodiments one or more rare earth layers enable a
transition from a semiconductor material of a first type and/or
composition and/or orientation to a semiconductor material of a
second type, composition and/or orientation; an embodiment is
depicted in FIG. 6a. As disclosed herein the rare-earth layers may
function as a transition layer(s) between, for example, a silicon
layer(s) and a germanium layer(s) such that the rare-earth layer(s)
acts as a sink for defects attempting to propagate from an initial
layer, optionally a silicon layer, to a final layer, optionally a
germanium layer, during a growth or deposition process. A REO
layer, operable as a transition layer, enables, for example, a
Si.sub.(1-m)Ge.sub.m layer to be grown or deposited on a different
composition Si.sub.(1-n)Ge.sub.n layer to a range thicker than the
conventional critical layer thickness hence enabling different
device structures; for example, one device may be a tandem solar
cell where more efficient absorption of a portion of the spectrum
not adsorbed by a first solar junction is enabled.
[0045] A growth or deposition process may be any one, or
combination, of those known to one knowledgeable in the art;
exemplary processes include CVD, MOCVD, PECVD, MBE, ALE, PVD,
electron beam evaporation, multiple source PVD. An exemplary
structure as shown in FIG. 9 may be a multiple-junction solar cell
wherein one region comprises a silicon p-n junction cell, a second
region is a rare-earth transition region functioning as a defect
sink and a third region is a germanium p-n junction cell;
optionally, a first or second region may be Group IV, Group III-V
or Group II-VI semiconductors.
[0046] In some embodiments a rare-earth layer transition region
comprises a first rare-earth portion of first composition adjacent
to a first semiconductor region, a second rare-earth portion of
second composition adjacent to a second semiconductor region and a
third rare-earth portion of third composition separating the first
and second rare-earth portion; in some embodiments the third rare
earth composition varies from the first rare-earth composition to
the second rare-earth composition in a linear fashion;
alternatively the third rare earth composition may vary in a
step-wise fashion; alternatively, the third rare earth region may
comprise multiple layers, each with a distinct composition
determined by a desired stress profile to facilitate the capture
and/or annihilation of lattice defects as may be generated by the
transition from the first and second semiconductor regions during a
growth process and subsequent process steps. In some embodiments a
third rare earth region may transition from a compressive stress to
a tensile stress based upon the beginning and ending
compositions.
[0047] High resolution transmission electron microscope image of
another optional embodiment of rare-earth atom incorporated in
silicon and/or silicon-germanium structures is shown in FIG. 94 of
U.A. 2008/0295879. The germanium and erbium fractions may be used
to tune the strain in the material. The Si/SiEr and Si/SiGeEr
layers demonstrate that Ge is effective in reducing dislocation and
threading dislocations vertically through the layers along the
growth direction.
[0048] Atomic and molecular interstitial defects and oxygen
vacancies in rare-earth oxide (REOx) can also be advantageously
engineered via non-stoichiometric growth conditions. The atomic
structure of singly and doubly positively charged oxygen vacancies
(O.sub.v.sup.+, O.sub.v.sup.2+), and singly and doubly negatively
charged interstitial oxygen atoms (O.sub.i.sup.-, O.sub.i.sup.2-)
and molecules (O.sub.2i.sup.-, O.sub.2i.sup.2-) can be engineered
in defective crystals of REO.sub.x=1.5.+-.y,
0.1.ltoreq.y.ltoreq.1). Singly and doubly negatively charged oxygen
vacancies (O.sub.v.sup.-, O.sub.v.sup.2-) are also possible.
Rare-earth metal ion vacancies and substitutional species may also
occur and an oxygen vacancy paired with substitutional rare-earth
atom may also occur. However, atomic oxygen incorporation is
generally energetically favored over molecular incorporation, with
charged defect species being more stable than neutral species when
electrons are available from the rare-earth conduction band.
Alternatively, nitrogen, N, or phosphorus, P, may replace the
oxygen or used in various combinations.
[0049] Nitrogen-containing defects can be formed during growth of
rare-earth-oxide using nitrogen and nitrogen containing precursors
(e.g., N.sub.2, atomic N, NH.sub.3, NO, and N.sub.2O). The role of
such defects using nitrogen in oxides leads to an effective
immobilization of native defects such as oxygen vacancies and
interstitial oxygen ions and significantly reduce the fixed charge
in the dielectric. Non-stoichiometric REOx films can be engineered
to contain oxygen interstitials, (e.g., using oxygen excess and/or
activated oxygen O.sub.2*, O*) and/or oxygen vacancies (e.g., using
oxygen deficient environment).
[0050] The process of vacancy passivation by molecular nitrogen is
also possible. Atomic nitrogen is highly reactive and mobile once
trapped in the oxide structure resulting in the more effective
passivation of oxygen vacancies. The REOx materials generate
positive fixed charge via protons and anion vacancies and can be
effectively reduced by introduction of atomic nitrogen and/or
molecular nitrogen.
[0051] Rare earth multilayer structures allow for the formation of
multiple semiconductor layers. Enhanced operating performance is
achieved compared to structures without rare earths. Alternatively,
in some embodiments, a first semiconductor layer may be
polycrystalline, large grained crystalline or micro/nano
crystalline; subsequent layers may also be polycrystalline, large
grained crystalline or micro/nano crystalline. As used herein,
large grained is defined as a grain of lateral dimension much
larger than the dimension in the growth direction.
[0052] In some embodiments a structure within a solid state device
comprises a first region of first composition, a second region of
second composition and a third region of third composition
separated from the first region by the second region; wherein the
second region comprises a first and second rare-earth compound such
that the lattice spacing of the first compound is different from
the lattice spacing of the second compound and the third
composition is different from the first composition; optionally, a
solid state device comprises a first and third region comprising
substantially elements only from Group IV; optionally, a solid
state device comprises a third region comprising substantially
elements only from Groups III and V; optionally, a solid state
device comprises a third region comprising substantially elements
only from Groups II and VI; optionally, a solid state device
comprises a second region described by
[RE1].sub.v[RE2].sub.w[RE3].sub.x[J1].sub.y[J2].sub.z wherein [RE]
is chosen from a rare earth; [J1] and [J2] are chosen from a group
consisting of Oxygen (O), Nitrogen (N), and Phosphorus (P), and
0.ltoreq.v, w, z.ltoreq.5, and 0<x, y.ltoreq.5; optionally, a
solid state device comprises a second region comprising a first
portion of fourth composition adjacent said first region; a second
portion of fifth composition; and a third portion of sixth
composition separated from the first portion by the second portion
and adjacent said third region wherein the fifth composition is
different from the fourth and sixth compositions; optionally, a
solid state device comprises a second portion comprising a first
surface adjacent said first portion and a second surface adjacent
said third portion and said fifth composition varies from the first
surface to the second surface; optionally a solid state device
comprises a second portion comprising a first surface adjacent said
first portion and a second surface adjacent said third portion and
comprises a superlattice with a structure comprising two layers of
different composition which repeat at least once; optionally a
solid state device comprises a first portion in a first state of
stress and a third portion in a second state of stress different
from the first state of stress.
[0053] In some embodiments a solid state device comprises first and
second semiconductor layers separated by a rare earth layer wherein
the first semiconductor layer is of composition X.sub.(1-m)Y.sub.m;
the second semiconductor layer is of composition X.sub.(1-n)Y.sub.n
and the rare earth layer is of a composition described by
[RE1].sub.v[RE2].sub.w[RE3].sub.x[J1].sub.y[J2].sub.z wherein [RE]
is chosen from a rare earth; [J1] and [J2] are chosen from a group
consisting of oxygen (O), nitrogen (N), and phosphorus (P), and X
and Y are chosen from Group IV elements such that 0.ltoreq.n,
m.ltoreq.1, 0.ltoreq.v, z.ltoreq.5, and 0<w, x, y.ltoreq.5 and
wherein n is different from m; optionally, a device comprises a
rare earth layer comprising a first and second rare earth layer
such that the composition of the first layer is different from the
composition of the second layer and the lattice spacing of the
first layer is different from the lattice spacing of the second
layer.
[0054] In some embodiments a solid state device comprises a first
semiconductor layer; a second semiconductor layer; and a rare earth
layer comprising regions of different composition separating the
first semiconductor layer from the second semiconductor layer;
wherein the rare earth layer is of a composition described by
[RE1].sub.v[RE2].sub.w[RE3].sub.x[J1].sub.y[J2].sub.z wherein [RE]
is chosen from a rare earth; [J1] and [J2] are chosen from a group
consisting of oxygen (O), nitrogen (N), and phosphorus (P), such
that 0.ltoreq.v, w, z.ltoreq.5, and 0<x, y.ltoreq.5 such that
the composition of the rare earth layer adjacent the first
semiconductor layer is different from the composition of the rare
earth layer adjacent the second semiconductor layer; optionally, a
device comprises first and second semiconductor materials chosen
from one or more Group IV elements or alloys of Group III-V
elements or alloys of Group II-VI elements; optionally, a device
comprises a rare earth layer comprising a superlattice of a
structure that repeats at least once; optionally, a device
comprises a rare earth layer comprising a first region adjacent
said first semiconductor layer, a second region adjacent said
second semiconductor layer and a third region separating the first
region from the second region such that the composition of the
third region is different from the first region and the second
region.
[0055] In some embodiments a structure within a solid state device
comprises at least two photovoltaic cells in tandem, the structure
comprising; a first solar cell of first composition comprising
first and second surfaces; a second region of second composition
comprising first and second surfaces; and a second solar cell of
third composition comprising first and second surfaces separated
from the first region by the second region the first solar cell and
second solar cell being arranged in tandem; wherein the second
region consists substantially of first and second rare-earth oxide
compounds such that the lattice spacing of the first rare-earth
oxide compound is different from the lattice spacing of the second
rare-earth oxide compound and wherein the first and second solar
cells consist substantially of elements only from Group IV and the
third composition is different from the first composition and the
first surface of the second region is in contact with substantially
all of the second surface of the first solar cell and the second
surface of the second region is in contact with substantially all
of the first surface of the third solar cell and wherein the
composition of the second region consists substantially of
[RE1].sub.v[RE2].sub.w[RE3].sub.x[J1].sub.y[J2].sub.z wherein [RE]
is chosen from a rare earth; [J1] is oxygen and [J2] is chosen from
a group consisting of Oxygen (O), Nitrogen (N), and Phosphorus (P),
and 0.ltoreq.v, z.ltoreq.5, and 0<w, x, y.ltoreq.5; optionally,
a solid state device comprises a second region comprising, a first
portion of fourth composition adjacent said first solar cell; a
second portion of fifth composition; and a third portion of sixth
composition separated from the first portion by the second portion
and adjacent said second solar cell wherein the fifth composition
is different from the fourth and sixth compositions; optionally, a
solid state device comprises a second portion comprising a first
surface adjacent said first portion and a second surface adjacent
said third portion and said fifth composition varies from the first
surface to the second surface; optionally, a solid state device
comprises a second portion comprising a first surface adjacent said
first portion and a second surface adjacent said third portion and
comprises a superlattice with a structure comprising two layers of
different composition which repeat at least once; optionally, a
solid state device comprises a first portion in a first state of
stress and said third portion is in a second state of stress
different than the first state of stress.
[0056] In some embodiments a solid state device comprises at least
two solar cells in tandem; the device comprising; first and second
semiconductor layers operable as solar cells in tandem separated by
a rare earth layer wherein the first semiconductor layer consists
of composition X.sub.(1-m)Y.sub.m; the second semiconductor layer
consists of composition X.sub.(1-n)Y.sub.n and the rare earth layer
is of a composition consisting substantially of
[RE1].sub.v[RE2].sub.w[RE3].sub.x[J1].sub.y[J2].sub.z wherein [RE]
is chosen from a rare earth; [J1] is oxygen and [J2] is chosen from
a group consisting of oxygen (O), nitrogen (N), and phosphorus (P),
and X and Y are chosen from Group IV elements such that 0.ltoreq.n,
m.ltoreq.1, 0.ltoreq.v, z.ltoreq.5, and 0<w, x, y.ltoreq.5 and
wherein n is different from m; optionally, a device comprises a
rare earth layer comprising a first and second rare earth layer
such that the composition of the first layer is different from the
composition of the second layer and the lattice spacing of the
first layer is different from the lattice spacing of the second
layer.
[0057] In some embodiments a solid state device comprises at least
two solar cells in tandem; comprising a first semiconductor layer
operable as a solar cell; second semiconductor layer operable as a
solar cell; the first semiconductor layer and second semiconductor
layer being arranged in tandem; and a rare earth layer comprising
regions of different composition separating the first semiconductor
layer from the second semiconductor layer; wherein the rare earth
layer is of a composition consisting substantially of
[RE1].sub.v[RE2].sub.w[RE3].sub.x[J1].sub.y[J2].sub.z wherein [RE]
is chosen from a rare earth; [J1] is oxygen and [J2] is chosen from
a group consisting of oxygen (O), nitrogen (N), and phosphorus (P),
such that 0.ltoreq.v, z.ltoreq.5, and 0<w, x, y.ltoreq.5 such
that the composition of the rare earth layer adjacent the first
semiconductor layer is different from the composition of the rare
earth layer adjacent the second semiconductor layer; optionally, a
device has a first and second semiconductor materials chosen from
one or more Group IV elements or alloys; optionally, a device has a
rare earth layer comprising a superlattice of a structure that
repeats at least once; optionally, a device has a rare earth layer
comprising a first region adjacent said first semiconductor layer,
a second region adjacent said second semiconductor layer and a
third region separating the first region from the second region
such that the composition of the third region is different from the
first region and the second region.
[0058] The foregoing described embodiments of the invention are
provided as illustrations and descriptions. They are not intended
to limit the invention to a precise form as described. In
particular, it is contemplated that functional implementation of
invention described herein may be implemented equivalently in
various combinations or other functional components or building
blocks. Other variations and embodiments are possible in light of
above teachings to one knowledgeable in the art of semiconductors,
thin film deposition techniques, and materials; it is thus intended
that the scope of invention not be limited by this Detailed
Description, but rather by Claims following. All patents, patent
applications, and other documents referenced herein are
incorporated by reference in their entirety for all purposes,
unless otherwise indicated.
* * * * *